Why is suction on my medela swing rubbish?

I have a medela swing which I got second hand. Worked great for a while but now suction is really hit or miss. I have taken it apart and reassembled, changed the little white membrane, ensured its all dry after being sterilised before using......still suction barely getting anything out.

We had an Ameda which was second hand, and while brilliant for a while it gradually lost suction and when we rang the manufacturers they were very honest and said they are not designed to last forever. If you are using it regularly (as we were, I pumped for hours for 5.5 months) it is probably just knackered so you will need to replace it. The motors in these things are not huge and so their lifespan is somewhat limited. Annoying when not cheap but a breast pump with rubbish suction is as much use as a choccy teapot

Have you changed the little white flap? It seems to work miracles. You might have a new one in the box it came with? These are also easily available through amazon, mothercare etc. Same thing happened with my swing.